1. Field of the Invention
The present invention relates to a method and apparatus for forming white inkjet images of excellent visibility on fabric.
2. Description of the Related Art
Titanium dioxide (TiO2) is well known as a white pigment with good hiding power, but titanium dioxide is also heavy, with a specific gravity of about 4.2. Consequently, when it is used as a pigment for a white inkjet ink, the pigment settles when the ink is allowed to stand for an extended period. Preventing this ink settling is difficult, and up to now it has been impossible to achieve adequate dispersion stability with an ink containing titanium dioxide.
Ink clogging and improper discharge can occur if the pigment in an ink settles in the ink passage within an inkjet head. Also, since titanium dioxide is a ceramic, it is extremely hard and accelerates wear to the nozzle portions of an inkjet head.
In view of this, it has been proposed that hollow polymer microparticles be used instead of titanium dioxide as the pigment for a white inkjet ink (Japanese Patent No. 2,619,677 and Japanese Patent Application Laid-Open No. 2000-103995). Hollow polymer microparticles have a specific gravity of close to 1 and therefore are not prone to settling, which solves the problem of ink clogging caused by the settling of pigment.
Nevertheless, even if a white inkjet ink containing hollow polymer microparticles as a white pigment is used, when a printed image is formed by a conventional ink-jet recording method on a dark-colored fabric, such as black T-shirt fabric, the visibility of the printed image is extremely poor because the ink penetrates into the fabric far more than into paper or a film.
In addition, an image printed on fabric needs to have good laundering fastness, but here again the required characteristics cannot be achieved with a conventional inkjet recording method.